The need for a method of temporarily supporting the semi-liquid material, generally known as concrete, while it is hardening, has existed almost as long as a self-hardening material (concrete or liquid stone) has been in existence. Some of the earlier patents such as that to Steiper, U.S. Pat. No. 827,268 show a removable method of fastening "flying scaffolding" to iron joist and here they taught fastening to "I" beams. Many, many ingenuous devices have been developed since that time with their ingenuity being directed to methods of removing the form after the material has hardened.
The following are listed as typical of those found in the art: Steiper, U.S. Pat. Nos. 827,268; Ducan, 1,502,092; Macomber, 1,796,851; Marks, 1,819,906; Selway, 1,625,056; Dell, 2,202,096; Faber, 2,218,705; Fribert, 2,297,952; Badt, 2,508,635; Olson, 2,575,678; Ledbetter, 2,609,585; Dreier, 3,093,932; Bowden, 3,130,470; Tooley, 3,294,357; Naillon, 3,341,639; Sullivan 3,405,903; Butts, 3,818,083; 3,189,143; 3,841,597; 3,845,594; 3,913,296; 3,945,168; and 4,015,396.
These patents show an orderly progression from inter-"I" beam bracing, for example, 1,652,056 to 2,609,585; then later with the beginnings of the development of bar joist formed devices, beginning with 2,297,952; through the bar lock devices such as shown in 3,945,168 and 4,015,396 and the various references that were cited in these patents.
This development from step to step clearly shows the effect of the economics of both the supply of materials and the reusability of some of the materials. Also reflected in the development is the increasing effect of labor, both on the shape of the device involved and the labor in assembling and disassembling the temporary form parts. Recently there has been developed the idea of secondary utility of the form parts after the temporary supports are removed. This is shown in devices such as shown in U.S. Pat. No. 3,341,639.